Only Admins can comment on objectionable pages when comments turned off

Bug 1310861

Currently if someone marks a page, that has comments set to off,
objectionable then eveyone that can access the page can now leave
comments.

Have adjusted it so that only admins can leave comments.

Change-Id: I82bd01814e73c39b056082965a6b483e6346a82f
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Only Admins can comment on objectionable pages when comments turned off"